Plant hormones have been intensively studied for decades for their diverse and complex effects on plant life. Of the five main hormones-auxins, ethylene, abscisic acid, cytokinins and gibberellins-the molecular signaling and mode of action of ethylene has been the most fully researched.
Ethylene (C2H4) is a gaseous plant hormone that affects myriad developmental processes and fitness responses in plants, such as germination, flower and leaf senescence, fruit ripening, leaf abscission, root nodulation, programmed cell death and responsiveness to stress and pathogen attack. Over the past decade, genetic screens have identified more than a dozen genes involved in the ethylene response in plants.
Ethylene and the ethylene response pathways govern diverse processes in plants, and these effects are sometimes affected by the action of other plant hormones, other physiological signals and the environment, both biotic and abiotic. For example, it is known that cytokinin can cause ethylene like effects through the action of ethylene. In addition, abscisic acid can inhibit ethylene production and signaling. Auxin and ethylene are also known to cooperate in various physiological phenomena. Such physiological activities of ethylene include, but are not limited to, promotion of food ripening, abscission of leaves and fruit of dicotyledonous species, flower senescence, stem extension of aquatic plants, gas space (aerenchyma) development in roots, leaf epinastic curvatures, stem and shoot swelling (in association with stunting), femaleness in cucurbits, fruit growth in certain species, apical hook closure in etiolated shoots, root hair formation, flowering in the Bromeliaceae, diageotropism of etiolated shoots, and increased gene expression (e.g., of polygalacturonase, cellulase, chitinases, β1,3-glucanases, etc.). Ethylene is released naturally by ripening fruit and is also produced by most plant tissues, e.g., in response to stress (e.g., drought, crowding, disease or pathogen attack, temperature (cold or heat) stress, wounding, etc.) and in maturing and senescing organs.
Ethylene is generated from methionine by a well-defined pathway involving the conversion of S-adenosyl-L-methionine (SAM or Ado Met) to the cyclic amino acid 1-aminocyclopropane-1-carboxylic acid (ACC) which is facilitated by ACC synthase. ACC synthase is an aminotransferase which catalyzes the rate limiting step in the formation of ethylene by converting S-adenosylmethionine to ACC.
Ethylene is then produced from the oxidation of ACC through the action of ACC oxidase (also known as the ethylene forming enzyme) with hydrogen cyanide as a secondary product that is detoxified by β-cyanoalanine synthase. Finally, ethylene can be metabolized by oxidation to CO2 or to ethylene oxide and ethylene glycol.
There is a continuing need for modulation of ethylene production and its response pathways in plants for manipulating plant development or stress responses. This invention relates to novel ethylene over-producer 1 (ETO1) sequences and their use in plants to inhibit ethylene production by removal of a critical component on the ethylene synthesis pathway. The invention includes novel polynucleotide sequences, expression constructs, vectors, plant cells and resultant plants. These and other features of the invention will become apparent upon review of the following materials.